Many type of electrical lamps require a gas fill at a precise pressure for optimum operation. Heretofore it has been the practice to check the internal lamp pressure by breaking the lamp bulb under water. The volume of water drawn into the bulb is measured when the pressure in the lamp is less than atmospheric pressure, or the escaping gas is funneled into a liquid-filled inverted graduated cylinder if the bulb were filled to a pressure above the atmospheric pressure. In this latter case, the gas will displace the water in the cylinder and can thus be measured.